C.sub.2 -C.sub.5 olefins are produced in various thermal and catalytic petroleum refining operations. To some extent these olefins can be employed in the production of petrochemicals. However, substantial quantities of these olefins must be utilized in the production of gasoline and/or distillate products.
The alkylation of isobutane with C.sub.3 and C.sub.4 olefins, for example, is widely practiced to produce high octane, low sensitivity gasoline. To a lesser extent polymerization processes are used to convert C.sub.2 -C.sub.5 olefins to higher boiling, more valuable hydrocarbon fractions. In some instances, various combinations of alkylation and polymerization are used to convert light olefins to gasoline and heavier hydrocarbons. The combination of alkylation and polymerization is particularly useful in those situations where isobutane is in short supply.
In the sulfuric acid alkylation of isobutane it is conventional to employ a C.sub.4 hydrocarbon mixture as a feed to the process. Refinery C.sub.4 hydrocarbon mixtures normally are comprised of isobutane, isobutylene, butene-1, butene-2 and normal butane. Isobutylene tends to produce inferior alkylation products, has the lowest yields, and has the highest acid consumption of any of the olefins present in the feed. Under such circumstances, it may be desirable to separate the isobutylene fraction from the feed by, for example, selectively dimerizing the isobutylene to produce a dimer having a high clear research octane number and high clear research and motor octane blending values.
In the hydrofluoric acid alkylation of isobutane, butene-1 and pentene-1 alkylate much less favorably with isobutane than the corresponding internal olefins. Therefore, it would appear to be desirable to isomerize the butene-1 and pentene-1 fractions prior to employing the olefins in the alkylation process. It is readily apparent that a single process which would selectively dimerize isobutylene while simultaneously isomerizing butene-1 to butene-2 and pentene-1 to pentene-2 would be highly desirable in preparing the feed to the alkylation process.
In Europe, the alkylation of light olefins is practiced to a limited extent because of the relatively moderate market for gasoline. However, propylene dimerization processes to make methyl pentenes are of interest to provide a high clear research octane front end gasoline blending component. Polymerization of C.sub.3 -C.sub.4 olefins to low pour oligomer distillates should become widespread as more and more propylene and butylene by-products become available from new ethylene plants.
Isobutylene and other olefins, particularly mono-1-olefins, have been polymerized utilizing a catalyst comprising a crystalline aluminosilicate in hydrogen form. It is also known that catalyst compositions such as the Y-zeolites can be employed for dimerizing isobutylene for short process periods. However, the useful lives of the prior art catalysts are limited by the formation of heavy polymer that is incapable of being diffused out of the active cage-like cavities wherein dimerization and subsequent trimerization, etc. occurs. Such catalysts after short polymerization periods contain large concentrations of heavier polymer, as measured by carbon value determinations made on the catalyst, and so become substantially inactive.